1. Field of the invention
The present invention relates to a controller for controlling the temperature of an injection cylinder in an injection molding machine.
2. Description of the Related Art
There is known an injection molding machine having a temperature regulator for regulating the temperature of an injection cylinder by PID feedback control. The temperature regulator carries out P (proportional), I (integral) and D (differential) control to regulate the calorific value of a heater for heating the injection cylinder so that the cylinder temperature agrees with the preset value. The parameter values used for this PID feedback control are set in advance before the injection molding operation is started. For the conventional temperature regulator for an injection molding machine, the PID parameter values set in advance cannot be changed during the operation of the injection molding machine. Therefore, if the setting of the PID parameters becomes improper due to a disturbance such as a change of molding temperature or ambient temperature during the operation of the injection molding machine, the PID parameter value must be set again by interrupting the injection molding operation. This delays the molding operation.
If the preset value of a PID parameter becomes markedly improper due to a disturbance, there occurs a great difference between the actual cylinder temperature and the preset cylinder temperature for a long period of time despite the fact that the feedback control itself functions normally. Therefore, molding defects such as short shot, burning, and sink mark are produced, by which a normal injection molding operation sometimes becomes impossible.
Also, it is difficult to determine the PID parameter by predicting the temperature rise, etc., caused by the shear compression of resin when it is measured and mixed, before starting a molding operation. Therefore, the PID parameter value set before the start of the injection molding operation cannot be guaranteed to be always proper for the actual injection molding operation.